The present invention relates to a method for processing ceramic components that have become contaminated by dust deposits, especially contaminated ceramic catalytic converters or catalyzers that remove nitrogen.
The present invention further relates to an apparatus for cleaning ceramic components that have been contaminated with dust deposits, especially contaminated ceramic catalyzers that remove nitrogen.
The invention will be subsequently explained in conjunction with ceramic catalyzers such as are used in nitrogen oxide reduction apparatus. However, the invention can be utilized anywhere where ceramic components are to be cleaned and processed after they have been contaminated by dust deposits.
The flue gases from power plants, refuse incinerators and the like must be cleaned before they can be released into the atmosphere.
A nitrogen removal stage is integrated into the cleaning process, during which the NO.sub.x is reduced by the addition of ammonia, and in particular in the presence of catalyzers. These catalyzers reduce the reaction temperature and accelerate the reduction process. They comprise ceramic material, the main substituent of which is titanium dioxide. The catalytically active material is vanadium pentoxide or tungsten trioxide.
The catalyzers comprise so-called catalyzer elements that are embodied as elongated honeycombed bodies and form separate, parallel flow channels having rectangular and generally square cross-sectional areas. The catalyzer elements are combined into modules, with each module having a steel frame into which the catalyzer elements are inserted parallel to one another.
By way of example, the power plant Bergkamen A (electrical capacity 750 MW) is provided with two nitrogen removing reactors that are provided with a total of 41,472 catalyzer elements, each of which has an external dimension of 150.times.150.times.840 mm. The total weight of the catalyzer modules is 800 t.
The useful life of the catalyzers is not unlimited. Rather, a deactivation occurs, whereby dust particles that contain noxious or harmful material are deposited upon the catalyzer walls. The rapidity with which this occurs depends upon at which location of the flue gas cleaning process the nitrogen removal is undertaken. Keeping this in mind, the most favorable location would be in an arrangement downstream of the flue gas desulfurization apparatus, but the flue gas temperature at this location is not sufficient for heating up the catalyzers to the reaction temperature. In this connection, a reheating of the flue gases would be necessary. To this extent, more favorable conditions are found in the vicinity of the boiler upstream of the air preheater. This involves the so-called high-dust control, with which, however, the degree of contamination of the catalyzer elements is the greatest.
By means of periodic intermediate cleaning, the useful life of the catalyzers can be extended. For this purpose, up to now so-called soot blowers in the form of traverse blowers have been used, which are integrated into the nitrogen oxide reduction apparatus. They comprise nozzle connections that are guided over the catalyzers and blow hot steam into the catalyzer elements. The traverse blowers represent a considerable capital expenditure for apparatus. Furthermore, the effectiveness of the cleaning also leaves something to be desired, since the blast energy is already dissipated after a few centimeters.
Finally, the catalyzer elements are spent and must be replaced.
The processing of the spent ceramic catalyzers represents a considerable problem. The catalyzers are ground, whereupon in principle the possibility exists for cleaning the ceramic material and reusing it as base material for the manufacture of catalyzers. However, the cleaning is extraordinarily expensive because with this type of reuse, the chemical properties of the material play the important role. In addition, the material is not refired, but rather is merely calcined at about 900.degree. C. and therefore receives a strength that is less than that of fired ceramic. Therefore, the up to now most frequently encountered alternative is to dispose of the spent and ground catalyzers in the contaminated state in dumps, or to supply it as an additive or filler to a slag tap furnace of a coal-fired power plant.